Sorry, but I can't agree. There are plenty of references to impromptu performances pre-1914 that were passionate, histrionic, mawkish and even angry - many where there was 'not a dry eye in the house'.
One of the problems with early recording equipment was a very limited range. One had to stand very close and keep to a level tone for the best results. And given that many of the early singers were probably rather wary of such a machine, their apparent 'stiffness' and lack of passion is easy to understand.
If you look at the time sigs in some of the transcripts of source material (I'm thinking of the Hammond and Gardner MSs, and songs like 'Hares in the Old Plantation') you can see that the singer adopted a very free and easy approach, which would indicate to me that there was a lot of ornamentation and the like going on.